Vacuum Rabi splitting is observed in a coupled qubit-resonator system consisting of a GaAs double quantum dot and a coplanar waveguide resonator. Derived values of the qubit-resonator coupling strength and the decoherence rate indicate strong couplin
g, which assures distinct vacuum Rabi oscillation in the system. The amplitude of decoherence is reasonably interpreted in terms of the coupling of electrons to piezoelectric acoustic phonons in GaAs.
